Tom Meinelt / Splash News 1 / 3
Tom Meinelt / Splash News 1 / 3

Charles Spencer couldn't be happier for his nephew Prince William, who welcomed his firstborn son with Duchess Kate at St. Mary's Hospital in London on Monday. "We're all so pleased," says Spencer, younger brother of the late Princess Diana. "It's wonderful news."

PHOTOS: Princess Diana's first pregnancy

Recalling his own sister's birth in July 1961, Spencer tells Us Weekly in a statement, "My father [John Spencer, 8th Earl Spencer] always told us how Diana was born on just such a blisteringly hot day, at Sandringham, in July 1961." Now that the Duke and Duchess of Cambridge are parents, he says, "It's another very happy summer's day, half a century on."

PHOTOS: Princess Diana's wedding to Prince Charles

Spencer, 9th Earl Spencer, has four children with ex-wife Victoria Lockwood: Lady Kitty Eleanor, 22, twins Lady Eliza Victoria and Lady Amelia, 21, and Louis Frederick John, Viscount Althorp, 19. He has two children with his second wife, Caroline Freud: The Hon. Edmund Charles, 9, and Lady Lara Caroline, 7.

PHOTOS: Kate's maternity style

After marrying Canadian philanthropist Karen Gordon in June 2011, Spencer, 49, and his wife welcomed Lady Charlotte Diana on July 30, 2012.

MORE FROM WONDERWALL:

Royal baby fans, media gather outside St. Mary's Hospital

Prince William and Duchess Kate's child: 10 perks of being the royal baby

Celebrities who share a birthday with the newest royal

Royal baby fun facts