Psylocke

Psylocke aka Elizabeth Braddock born bit after midnight on April 23, 1956? Making her ~same age as Jean Gray at issues they're in together.

Captain Britain aka Brian Braddock is her twin brother, same birth date?

Omnibus
April 23, 1956 - Betsy and Brian Braddock are born. Captain Britain #1, 1985

Sept 9, 1982 - Brian Braddock returns to the 616. Betsy interrupts his evening tea, shows off her new purple hair. Daredevils #3

between Jan 10, 1983 and Mar 18, 1984 - Meggan states her family's kept her hidden from the public for 17 years and that she's a mutant. Mighty World of Marvel #7 and #14, respectively.

June 6, 1984 - After the loss of her lover and recovering from time in a concentration camp, Betsy tells Brian she's learned to focus her pain to strengthen her powers. Mighty World of Marvel #16