Pleydell-Bouverie was the eldest son of Jacob Pleydell-Bouverie, 4th Earl of Radnor, by his wife Lady Mary Augusta Frederica Grimston, daughter of James Grimston, 1st Earl of Verulam.
plˈeɪdɛlbˈuːvɚɹi wʌzðɪ ˈɛldɪst sˈʌn ʌv dʒˈeɪkəb plˈeɪdɛlbˈuːvɚɹi, fˈoːɹθ ˈɜːl ʌv ɹˈædnɚ, baɪ hɪz wˈaɪf lˈeɪdi mˈɛɹi ɔːɡˈʌstə fɹˈɛdɚɹˌɪkə ɡɹˈɪmstən, dˈɔːɾɚɹ ʌv dʒˈeɪmz ɡɹˈɪmstən, fˈɜːst ˈɜːl ʌv vˈɛɹuːlˌæm.