When she was nursing the twins, Fëanáro finally asked Nerdanel which one she meant would be Ambarussa, she replied, "They are both Ambarussa."
He said in exasperation, "Nerdanel, you cannot give them both the same name."
She firmly claimed that while she suspected there had been two, their fëa were born as one, for each one were born with half the amount an Elfling should have received and therefore cannot be balanced without the other.
Perhaps, as a mother, she was right…but Fëanáro, on the other hand, believed that the twins would grow to become two separate individuals and each should deserve to have their own name.
When he told her this, she was drifting off, eyes drooping closed with exhaustion, her arms growing slack from carrying the babies, so Fëanáro quickly moved to take the twins from her arms and put them to bed.
Just as he touched them, Nerdanel suddenly gasped, eyes flying open with horror, and tightened her arms around the twins.
Fëanáro was startled by her reaction, and even more so when she pulled their sons further away from his outstretched hands, looking at him with a haunted wariness she had never given him before.
"One will be Umbarto," she rasped, trembling, face pale with sweat, gray eyes alit with fey-like distant silver many said Fëanáro often possessed, "and only time will tell which one!"
'Ill-fated' the name meant, and Fëanáro felt a foreboding confusion, then a suddenly blaze of anger towards his wife, followed by that sudden, fierce, and desperate protectiveness over his youngest sons, from his own wife and their own mother.
This made him continue to reach for them, to practically wrestle them away from Nerdanel, but she also fought to keep them away from him for some reason…almost as if she was trying to protect their babies from him.
Still hurt and confused, his hands still gripping their blankets almost desperately, even as the babies started to whimper into tiny cries, Fëanáro replied in a trembling growl, "You mean one will be Ambarto!"
'High-exalted,' it meant, but while Nerdanel's doubt was clear in her eyes, she finally, and reluctantly, reliquished the twins to him (much to his relief), and whispered with a haunted sorrow, "It matters not."
